> On Mon, Jan 05, 2015 at 01:20:57PM +0000, David Laight wrote: > > > +/* simplify initialization of mask field */ > > > +#define CYCLECOUNTER_MASK(bits) (cycle_t)((bits) < 64 ? > > > ((1ULL<<(bits))-1) : -1) > > > > That has me chasing through the C integer promotion rules. > > Better might be: > > ((bits) < 64 ? (1ULL << (bits)) - 1 : (((1ULL << 63) - 1) << 1) + 1) > > I actually suspect there is a standard definition somewhere? > > This is an exact copy of CLOCKSOURCE_MASK, and if wrong, then both are > wrong. In any case, I can't see any issue here. Is not > > (some_int_type) -1 > > always equal to > > 0xf...(width of type) > > for all integer types, when using 2s compliment?
As I said, it leaves me chasing through the promotion rules (which I probably know if I actually think hard enough). Thinking... ~0ULL would be nice and simple and correct. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/